Figure 9. Long-skip distances and wobble differentially reflect molecular activity.

Reactive spheres were simulated with S = 50 s⁻¹, R = 4.9 µm, 1×n_L° = 90 sites/µm², and n_R° = 95 sites/µm². Association kinetics were governed by (1) or (2). Catch-slip parameters regressed from Marshall et al. [5],[32] were used in the catch-slip model, (4), or the just the high-impedance pathway parameters were entered into the slip model, (3). (A) The long-skip distance calculated from the two-parameter Poisson regression at a variety of ligand concentrations. Black circles: the catch-slip model was assumed with contact patch confinement. Blue triangles: the catch-slip model was assumed with molecular area confinement. Red squares: the slip model was assumed with contact patch confinement. Green diamonds: the slip model was assumed with molecular area confinement. Error bars show the 95% confidence interval estimate from the nonlinear regression. Surprisingly, the dissociation model had a moderate effect on the skip distance at low site densities but the confinement model had little effect. (B) The sample-normalized autocorrelation of the velocity component perpendicular to the flow direction (wobble velocity autocorrelation) was calculated and averaged together for the three simulated beads at each condition. The colors indicate the same reaction assumptions as in the previous graph. Heavy dashed lines: results from 4×90 sites/µm² ligand density. Intermediate dot-dashed lines: results from 1×90 sites/µm² ligand density. Light solid lines: results from ½×90 sites/µm² ligand density. Colors represent the same cases as in (A). The confinement model had the largest effect on the wobble autocorrelation.